1. Field of the Invention
The present invention relates to a motor control apparatus and a control method thereof, and more particularly, to a motor control apparatus and a control method thereof changing an overcurrent, which is generated in the motor, consumed by a brake resistor according to a rotation speed of the motor.
2. Description of the Related Art
A three-phase motor has a coil with a triangular winding. A motor control apparatus 300 for supplying AC power to drive a motor 100, as shown in FIG. 1, comprises a rectifying circuit part 110 to rectify commercial AC power (110V/220V) supplied from an AC power supply 200, and an inverting part 120 inverting the commercial AC power rectified by the rectifying circuit part 110 to AC power having various frequencies and supplying the AC power having the various frequencies to the motor 100.
The rectifying circuit part 110 generally comprises a diode rectifying circuit 111 rectifying the commercial AC power (110V/220V) supplied from the AC power supply 200 into DC power, and a capacitor 113 smoothing the DC power rectified by the diode rectifying circuit 111 into a predetermined voltage and transmitting the smoothed DC power to the inverting part 120.
The inverting part 120 comprises a bridge circuit provided with a plurality of first switching units 121, each having a first transistor 121a, and a first diode 121b connected to each other in parallel and a plurality of second switching units 123, each have a second transistor 123a and a second diode 123b. Respective ones of the first and second switching units 121 and 123 are provided in pairs in respective bridges of the bridge circuit, and tap nodes between the first and second switching units 121 and 123 of each of the respective bridges are connected to respective motor windings of the motor 100 via power input ends 100b of the motor 100.
The first and second switching units 121 and 123 are turned on and off by a switching controller 140 to provide the AC power having the various frequencies to supply to the motor 100.
A conventional motor control apparatus may comprise a dynamic braking circuit 130 performing a dynamic braking operation. The dynamic braking circuit 130 comprises a pair of brake relays 131 producing an open circuit or a short circuit in the motor windings of the motor 100, and three brake resistors 133 connected to each motor winding to consume an overcurrent generated in the motor 100 when the motor 100 brakes. The brake relay 131 is turned on when the motor 100 brakes or when the motor 100 stops, and short circuits the motor windings of the motor 100 by being turned on, to suddenly brake the motor 100 or to prevent the motor 100 from rotating by an external force when the motor 100 is stopped. The overcurrent generated from the motor windings when the motor 100 suddenly brakes is consumed through the brake resistors 133 so that the motor 100 or the brake relays 131 is prevented from breaking down by the overcurrent.
According to the conventional motor control apparatus 300, a resistance of the brake resistors 133 to consume the overcurrent generated when the motor 100 suddenly brakes depends on the overcurrent generated when the motor 100 brakes. For example, if a rotation speed of the motor 100 is high, the overcurrent generated when the motor 100 brakes is high so that high-resistance resistors are used as the brake resistors 133. If the rotation speed of the motor 100 is low, the overcurrent generated when the motor 100 brakes is low, so that low-resistance resistors are used as the brake resistors 133.
The low-resistance resistors are relatively advantageous for the dynamic braking circuit 130 to perform the dynamic braking operation, compared with the high-resistance resistors. The reason is that when the dynamic braking operation short circuits the motor windings of the motor 100 such that the resistances of the motor windings are close to “0”, an effect thereof is maximized with low resistance resistors. Thus, when the high-resistance resistors are used as the brake resistors 133, an operational effect of the dynamic braking operation is decreased. However, when the low-resistance resistors are used as the brake resistors 133, the motor 100 or the brake relays 131 may be damaged by the overcurrent generated when the motor 100 brakes.